The present invention relates to a device for controlling and signalling the operation of vacuum cleaners.
In a known device of this kind (DE-OS 30 30059), a vacuum cleaner which is to be controlled so that a constant rate of air flow is maintained, has a small air turbine arranged in its intake area. This air turbine serves as the sole external sensor and drives a tachometer which generates a control voltage that must be rectified. The control voltage is supplied to a phase control for the blower motor of the vacuum cleaner so that when the rate of air flow decreases, the phase control causes the output of the electric motor driving the blower of the vacuum cleaner to increases.
If the rate of air flow through the vacuum cleaner exceeds the preset constant air flow, the phase control acts to reduce the power of the blower motor.
However, a problem of this known device is that the air turbine is located in the path of the air flow drawn in by the vacuum cleaner, which, of course contains dust particles. These dust particles cannot be eliminated, not even by making the surfaces in the air turbine area as smooth as possible. Thus dust particles will gradually accumulate in certain areas and restrict the air passage. The dust particles, which may in some cases contain or consist of greasy or so liquid substances, will eventually limit or generally restrict the air passage, at least in the mechanical turbine area, to such an extent that the air turbine can no longer function properly, or so that considerable inaccuracy in the measured results will occur.
This problem is further aggravated by the fact that the air turbine drives a tachogenerator, in the form of an electric generator, with the blade element mounted on the shaft driving a generators rotor.
The operation of an air-flow sensor such as that described above, is necessarily problematic because power is required for driving the generator, for example, in order to overcome the friction between the collector and the carbon brushes and, generally, in order to induce the desired electric voltage in the stator windings via the rotating magnetic fields.
Consequently, the air flow sensor is neither non-reactive nor capable of providing true and correct information on the actual rate of air flow. The sensor itself interferes with the accuracy of the measured rate by its behavior and is, therefore, not capable of providing sufficiently exact results in areas of low air flows. This is due to the two reasons described before, i.e. clogging by dust particles, which leads to changes in the measured results due to aging, and undesirable frictional effects in the rotor area.
In order to enable a vacuum cleaner to be controlled so that a constant air flow rate is maintained or, correspondingly, a constant vacuum, it has also been known (DE-OS 24 43 945), to arrange a plurality of push buttons directly at the vacuum cleaner, for manual operation. These push buttons interlock each other and produce a mechanical effect only insofar as they act as a bypass to introducing additional air into the vacuum area of the vacuum cleaner so that the vacuum which is produced can be regulated in increments. The vacuum produced remains constant within larger limits by taking in amounts of additional air corresponding to the drop in the air flow rate, which would normally be described as secondary air. However, such a device requires that the bypass air flaps, normally arranged in the handle of the vacuum cleaner, be set by the operator to the correct position manually and this normally cannot be expected.
Normally, it would seem desirable to have the operation of the vacuum cleaner controlled largely automatically and to spare the operator the required decisions. The operator would then, conveniently, only have to determine certain desired properties, for example, the nature of the floor or the desired power setting (soft stage; maximum stage). The vacuum cleaner would then be controlled according to these preset values or operate along corresponding characteristics, in which case it may also be convenient to have the blower of the vacuum cleaner controlled by microprocessors, minicomputers or similar regulating or control components which are finding more and more acceptance in the field of household appliances.
However, to ensure perfect operation, such logical control centers require very comprehensive actual-value information including, if possible, information on the actual fill level of the dust bag, information on clogged pipes or secondary-air openings, or the like. The availability of this information permits the central control element to inform the operator accordingly, for example via a suitable display at the vacuum-cleaner body.
For indicating the fill level of the dust bag of a vacuum cleaner it has further been known (DE-PS 27 12 201 and DE-PS 28 35 473) to provide pressure switches reacting to pressure variations, usually in the form of minimum pressure governors, especially in the air intake area of the vacuum cleaner, and to advise the user, by externally visible pilot lamps, at least when the dust bag must be changed.
The fundamental principle of the fill level indication for vacuum cleaners is that as long as the dust bag is empty or only partially filled, a vacuum prevails in the area of the vacuum cleaner, basically at any point. A pressure difference sufficient for the intended measuring and indication purposes exists between this vacuum and the vacuum prevailing with a full or empty dust bag, provided a sufficiently sensitive pressure sensor or a pressure switch is used. In detail, the process may operate in such a way that the vacuum generated by the blower of the vacuum cleaner with an empty or partially filled dust bag is comparatively low. The air drawn in for cleaning purposes, for example through the floor brush of the vacuum cleaner, still has a comparatively free passage through the dust bag, so the resulting vacuum is only low, at high velocity, i.e. only a little below the atmospheric pressure, for example.
This situation changes, however, as the dust bag gradually becomes clogged, whereby a constantly increasing resistance to air flow is built up leading to a clear rise in vacuum at the motor side. As a result thereof, the work output of the vacuum cleaner drops altogether, as the higher vacuum prevails only in the area between the dust bag and the blower of the vacuum cleaner, not between the floor brush and the dust bag, for example. Consequently, the air-flow volume and the vacuum prevailing at the floor brush drop in this area.
Sufficiently sensitive diaphragm minimum pressure governors are capable of detecting safely the resulting pressure differences which, regarded alone and in absolute values are extremely small, for example in the range of approx. 25 mbar, between the empty and full dust bag, and of causing a signal to be generated when the dust bag is full or almost full. Then, the dust bag can be changed as required, it being simultaneously ensured that full use can be made of the cleaning possibilities provided by the vacuum cleaner and that environmental disturbance is minimized.
However, certain problems may be encountered with special types of vacuum cleaners when for some reason or other the vacuum difference between the empty and the full dust bag is either extremely small or missing and noticed only when the dust bag is already excessively full, or when in case of such vacuum cleaners, which anyway react critically to pressure measurements, producing excessively small pressure differences due to their particular design, it is desired to indicate additional peripheral marginal conditions, for example clogged pipes or a larger secondary-air opening, for example if the housing of the vacuum cleaner has not been fully closed.
It is the object of the present invention to provide control means for a vacuum cleaner which includes means for indicating the operational behavior of the vacuum cleaner and which ensures its controlled operation within a broad sensitivity range.
The invention solves the above mentioned problems with the aid of the characterizing features of claim 1 and provides the advantage that by measuring the air flow rate directly a primary actual value connected with the operation of the vacuum cleaner is used for interpreting its working conditions. It is possible, due to the sensitivity of the measurement, to obtain very exact measurements over the full working range of the vacuum cleaner when the air flow rate is, of small or extremely small. This information for regulate the operation of the vacuum cleaner and/or to indicate it to the user by optical and/or acoustic means.
It is, therefore, particularly advantageous to arrange a propeller for directly detecting the air-flow rate, i.e. responding to the incoming air flow, in the exhaust air flow of the vacuum cleaner, i.e. downstream of the dust bag and the blower of the vacuum cleaner. This area may be additionally calmed by intermediate filters. Since the air channel through the vacuum cleaner is enclosed on all sides, the exhaust air must be a true mirror image of the supply air flow drawn in. Consequently, the propeller element must also be in a position to react with particular sensitivity to a broad range of air-flow conditions prevailing in the vacuum cleaner so that it is possible, for example, to also indicate the fill level of the dust bag as percentage values, for example by means of a 7-segment luminous indication or a thin-film crystal indication.
According to one preferred embodiment of the present invention, the propeller can rotate freely and is arranged in the exhaust air flow of the vacuum cleaner, with the least possible frictional resistance. The frictional resistance in this embodiment results only from propeller's own support. The rotary movement of the propeller is recorded in a non-contact manner and converted into an electrical signal. This ensures that a true image of the exhaust air flow rate, even in the case of extremely low velocities, is supplied in the form of an electric signal sequence. It is made possible in this case, by supporting the propeller element in a suitable manner, to operate practically in a non-reactive manner, i.e. without any frictional effects. This can be achieved, for example, by using suitable plastic bearings or ball bearings support the propeller element or turbine wheel either centrally or from both sides, and by picking up the rotary movement separately, in a non-contact manner, for example via a light barrier arrangement which picks up and responds to the passage of a disk moving in the air current.
Non-contact scanning of the rotary movement of the propeller element can be achieved also by the use of other systems, operating, for example, on an inductive or capacitive basis (approximation switches), or by the use of Hall generators.
It is thus possible, in a very advantageous manner, to generate an output signal varying linearly with the exhaust air flow rate. This signal can then be evaluated in a suitable manner.
Since the measured air-flow rate (and the pressure conditions) of the vacuum cleaner are directly related to values such as the fill level of the dust bag, clogged pipes, open vacuum cleaner housings, and the like, it is possible, with the aid of the output voltage generated by the propeller element, to draw conclusions regarding the operating conditions of the vacuum cleaner prevailing at any given time. Consequently, it is also possible to define a threshold value for determining the moment when the flow rate recorded by the propeller element of the exhaust air sensor has dropped to a value indicating that the dust bag is full or almost full, in which case the fact that the dust bag has to be changed will be indicated. A similar effect, i.e. drop of the exhaust air flow rate, will be produced by clogged pipes so that this condition, too, can be detected by the air turbine. The opposite condition, namely an excessively high exhaust air flow rate, may occur, for example, when no dust bag is in place or when secondary air is introduced. This condition can also be recorded and evaluated, by use of suitable threshold means to provide a visual or acoustic signal which may include additional information on the prevailing pressure obtained by additional measurements.
According to an advantageous improvement of this embodiment, luminous diodes may be used for supplying a so-called YES/NO indication, by using suitable colors, for example red for the indication "defective or full dust bag" and green for "undisturbed operation".
The features described by the dependent claims permit additional advantageous improvements and further developments of the control and indication device for the operation of a vacuum cleaner. A particularly advantageous solution may be obtained by the simultaneous use of suitable pressure sensors at suitable points in the air passage, i.e. upstream of the dust bag, between the dust bag and the blower, or downstream of the blower in the exhaust air area, for deriving additional actual-value information in the form of vacuum values, which is then supplied to a central control circuit. The latter may then determine, for example automatically, whether or not the given fill level requires the immediate change of the dust bag or if the power loss can still be compensated by increasing the blower output, which would then have to be effected as required. It would also be possible in this connection for the control circuit, which would preferably comprise a microprocessor, to switch over the vacuum cleaner to different operating conditions as a trial, and to compare the actual values (air turbine output voltage and/or the pressure values supplied by pressure sensors) with stored values for deriving conclusions as to the actual condition of the vacuum cleaner. The conclusions arising from this comparison can then be used either for regulating the operation of the vacuum cleaner or for providing the operator with the corresponding information.
A vacuum cleaner equipped in this manner is capable either of regulating itself automatically to a constant air-flow rate or of adapting itself automatically, within the limits of predetermined power values or along predetermined characteristics, to the properties of the floors to be cleaned, which may also be determined by the vacuum cleaner automatically, with the additional possibility to have corresponding values preset by the user, for example if he wants to clean curtains, deep-pile carpets, plain linoleum floor coverings, or the like.